(a) Field of the Invention
The present invention relates to an illuminating device for slit lamp microscopes wherein rays from a light source are so made as to be able to be incident upon an object to be examined diagonally from above or below with respect to the optical axis of the objective.
(B) Description of the Prior Art
A slit lamp microscope whereby such transparent object as a cornea or crystalline body of an eyeball is optically cut by being illuminated with strong slit rays in a diagonal direction so that any minute abnormality within the transparent object may be exposed by diffused rays from fine substances in the transparent body structure and may be magnified and observed with a binocular stereoscopic microscope is so effective to ophthalmic diagnoses as to be already extensively used.
FIG. 1 shows a typical constitution of this kind of known illuminating device for slit lamp microscopes. In the drawing, reference numeral 1 indicates a light source, numeral 2 indicates a condenser lens, numeral 3 indicates a slit arranged on the optical axis of the condenser lens, numeral 4 indicates an objective, numeral 5 indicates reflector so arranged as to be at an angle of 45 degrees with the optical axis of the objective 4, numeral 6 indicates an object to be examined by observation, that is, an eyeball of a patient and numeral 7 indicates a microscope arranged on the side opposed to the side on which the eyeball 6 is located with respect to the reflector 5 on the extension line of the optical axis from the reflector 5 to the eyeball 6. The slit 3 and the surface of the eyeball 6 are conjugate with each other with respect to the objective 4. Therefore, rays issued from the light source 1 pass through the condenser lens 2 and reach the eyeball 6 through the slit 3, objective 4 and reflector 5 and produce a slit image at a point S on the eyeball 6. As a result, the cornea and others of the eyeball 6 are optically cut and are magnified and observed with the microscope 7. In such case, as the direction of the rays from the light source 1 is changed by 90 degrees by the reflector 5, the rays will be incident upon the eyeball 6 in the horizontal direction and, if the reflector 5 is not present, the image of the slit 3 will be produced at the imaginary conjugate point S'. The distances from the reflector 5 to the points S and S' are equal to each other. By the way, such slit lamp microscope as is shown in FIG. 1 is so made that the rays may be incident upon the eyeball 6 diagonally from the right or left by being rotated in a horizontal plane with the point S as rotating center.
As described above, according to this kind of illuminating device for slit lamp microscopes, the rays are incident upon the object to be examined in the horizontal direction and the object to be examined can be optically cut in various directions in the horizontal plane by moving the slit rays to the right and left in the horizontal plane. Depending on the condition of the disease of the eye of the patient, it is required to optically cut the object to be examined in various directions diagonally above or below the horizontal plane by moving the slit rays up or down with the point S as a center. The first type of illuminating device which can meet such requirement is shown in FIG. 2. That is to say, the first type of illuminating device for slit lamp microscopes is so arranged to observe the eyeball 6 with the microscope 7 that the entire illuminating optical system including the light source 1, condenser lens 2, slit 3 and objective 4 may be moved in a plane parallel with the paper surface (for example, from the position shown by the chain lines to the position shown by the solid lines) with an axis 8 provided in the position of the imaginary conjugate point S' as a center without moving the reflector 5 and microscope 7 and the slit rays may be thereby incident upon the eyeball 6 diagonally from below or above without varying the light path length. However, in the case of this system, there are defects that the entire comparatively large and heavy illuminating device must be inclined, that therefore a considerable strength and size are required for the supporting mechanism and that the entire slit light microscope apparatus must be large.
The second type of known illuminating device which can meet the above mentioned requirement is shown in FIG. 3. The second type of illuminating device for slit lamp microscopes is arranged as mentioned below. That is to say, a microscope 10 is so held that the optical axis between it and an eyeball 9 may be horizontal with the eyeball 9, and a reflector 11 so arranged as to be movable vertically to the optical axis between the eyeball 9 and microscope 10 and to be at an angle of 45 degrees with the optical azis as shown by the chain line in the normal state but to vary in the angle of inclination when moved vertically is provided between the eyeball 9 and microscope 10. Rays from a light source not illustrated reach the reflector 11 through an objective 12 vertically to the above mentioned optical axis from below and are reflected there to be directed to the eyeball 9. The objective 12 is divided into a group 12a on the side near to the reflector 11 and a group 12b on the side near to the light source and the rays between both lens groups 12a and 12b are so made as to be parallel rays. The lens group 12a is also so arranged as to be able to be lowered to the solid line position from the chain line position simultaneously with the lowering of the reflector 11 from the chain line position to the solid line position while varying its angle of inclination so that the distance from the lens group 12a to the reflector 11 and the distance from the reflector 11 to the eyeball 9 may be equal to each other, for example, to make the slit rays incident upon the eyeball diagonally from below. Thus, according to the second type, there are defects that, simultaneously with the vertical movement of the reflector 11 while varying its angle of inclination, the lens group 12a must be moved vertically by the corresponding distance as operatively connected with this movement and that therefore a very complicate operatively connecting mechanism is required.